1. Field of the Invention
This invention relates to preparation of catalysts such as those that are frequently employed to convert synthesis gas to an alcohol. More particularly, this invention relates to an improved process to dry the precipitated catalyst precursor attained during production of such catalysts to form a free-flowing particulate catalyst precursor having a reduced propensity for oxidation and self-heating on exposure to air, which would lead to decreased catalyst activity and selectivity to desired alcohols.
2. Background of the Art
Catalysts including molybdenum, sulfur and, optionally, cobalt have been found to be useful to convert synthesis gas to an alcohol. Synthesis gas is a mixture of carbon monoxide and hydrogen and is one of the most readily available starting materials for production of alcohols. These alcohols may include, in non-limiting example, ethanol and propanol. The molybdenum sulfide-based catalysts have been found to be very important in increasing both the alcohol production rate and yield, but processes to produce the catalysts themselves at large scale (metric tons and above) have often faced problems. These problems include, in many cases, a wet filter cake that is difficult to handle and/or dried catalyst precursor that may undergo oxidation and self-heating which leads to a decline in activity.
Thus, those skilled in the art have sought an effective method to convert a wet filter cake to a useful final catalyst that has performance at commercial scale that is comparable to that attained at laboratory scale. For example, United States Patents U.S. Pat. No. 4,752,623 to Stevens et al. and U.S. Pat. No. 4,825,013 to Quarderer et al. both describe processes for drying various catalyst preparations that include cobalt and molybdenum that include heating at 500° C. in an inert atmosphere such as nitrogen.
Unfortunately, when used to produce large volumes of catalyst for pilot scale or commercial scale production (0.1-100 metric tons (mT)), these methods may still result in catalyst precursors that suffer thermal run-away by oxidation. This oxidation may lead to creation of oxy-sulfide and oxide phases, which in turn reduce the catalyst's selectivity toward alcohols. These phases are not easily sulfided back to the active catalyst phase, even with a separate additional sulfiding procedure. Furthermore, at various points in these processes the catalyst precursors may be either too wet, such that the particles stick together and do not flow, or they are dried to a point of extremely low moisture content (for example, less than 1 weight percent), which makes them more easily auto-oxidized and more likely to suffer thermal run-away. Thus, there continues to be a need in the art for processes to prepare these catalysts that avoid the problems cited hereinabove.